Engine brakes or retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Engine brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, the hauling capacity of tractor-trailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in today's heavy vehicles.
Problems with existing engine braking systems include high noise levels and a lack of smooth operation at some braking levels resulting from the use of less than all of the engine cylinders in a compression braking scheme. Also, existing systems are not readily adaptable to differing road and vehicle conditions. Still further, existing systems are complex and expensive.
Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor.
U.S. Pat. No. 3,220,392 issued to Cummins on Nov. 30, 1965, discloses an engine braking system in which an exhaust valve located in a cylinder is opened when the piston in the cylinder nears the top dead center (TDC) position on the compression stroke. An actuator includes a master piston, driven by a cam and pushrod, which in turn drives a slave piston to open the exhaust valve during engine braking. The braking that can be accomplished by the Cummins device is limited because the timing and duration of the opening of the exhaust valve is dictated by the geometry of the cam which drives the master piston and hence these parameters cannot be independently controlled.
In conjunction with the increasingly widespread use of electronic controls in engine systems, braking systems have been developed which are electronically controlled by a central engine control unit which optimizes the performance of the braking system. Examples of these are disclosed in Pitzi U.S. Pat. No. 5,012,778; Faletti et al. U.S. Pat. No. 5,255,650; and Sickler U.S. Pat. No. 4,572,114. The electronic control units disclosed in the above-listed patents also control the injection of fuel in connection with the operation of the braking system.
U.S. Pat. No. 4,188,933 issued to Iizuka on Feb. 19, 1980, discloses an apparatus for controlling fuel injection and engine braking. During engine fueling, a fuel injection control unit develops a signal to activate a fuel injection valve for each cylinder. A load detection device provides a signal to activate a series of solenoid switching valves associated with inlet and exhaust valves when braking is demanded. The signal provided by the load detection device also energizes a relay which disconnects the fuel injectors from the fuel injection control unit, thereby preventing engine fueling during periods of engine braking.